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A. Magnetic resonance imaging (MRI) relies on magnetic fields and pulsed radio waves to produce an image. Unlike X-rays, it does not use ionizing radiation. Alexander Guimaraes, a radiologist at the Martinos Center for Biomedical Imaging at Massachusetts General Hospital, says that there have been no documented long-term health effects from exposure to MRI.

“We have people here that have spent hundreds of hours in the MRI,” he says, and studies have not found any signs of cancer, health problems, or cognitive damage from the technology.

Furthermore, Guimaraes explains, each MRI machine has strict safeguards in place to prevent it from delivering too much energy to the body, and “it’s impossible for it to run in a non-safe way.”

Some patients may be injected with contrast agents that allow the radiologist to better see structures inside the body. These agents have been linked to a rare condition called nephrogenic systemic fibrosis (NSF) in people with existing kidney disease. A blood test can help determine how well patients’ kidneys function and identify those at risk.

Another safety concern is implanted electronic devices or metallic objects in the body, many of which cannot be present in the scanner. The powerful magnet also transforms any nearby magnetic objects into dangerous projectiles, and safety precautions are taken to ensure none are present. Finally, some people feel claustrophobic or anxious in the scanner; they can receive a mild sedative beforehand, and patients have access to an alarm or buzzer to alert clinicians if needed.